P2531

Ignition Switch Run Pos Circ Low

Indicator

The PCM has detected a malfunction in the ignition switch run position circuit. The ignition switch supplies voltage to the PCM, ignition, and fuel delivery systems.

Code Set Parameters

The average PCM is programmed to expect an input reference voltage that is comparable to battery voltage (12.6-volts). If the input voltage signal falls below a specified minimum, a code will be stored and a service engine soon lamp may be illuminated. Some vehicles require multiple failure cycles in order for the service engine soon lamp to be illuminated; other will illuminate the service engine soon lam on the initial failure.

Symptoms

Symptoms may include a no start (or delayed start) condition, service engine soon lamp illumination, and a stored code. A red charging system failure indicator lamp may also accompany this code.

Common Causes

By far the most common cause of this code is from a misadjusted or defective ignition switch. Other causes may include a defective ignition switch, burned fuses or fusible links, a bad battery, alternator, open, shorted, corroded, or otherwise damaged wiring and/or electrical connectors. Technicians also report the presence of excessive corrosion on the battery cables as the cause of this code being stored.

Common Misdiagnosis

The battery is frequently replaced in error when the alternator or ignition switch are at fault.

Diagnosis

The ignition switch is used to transfer voltage from the battery and cables to virtually every system in the vehicle

Voltage transferred through the ignition switch is typically referred to as "switched voltage." In most cases, a mechanized actuator is turned using a keyed cylinder

The actuator turns (or slides) an electronic ignition switch that is composed of heavy grade contacts that are capable of withstanding high current draw

Battery voltage is supplied to the input side of the ignition switch via fused primary wiring and cables

When the ignition switch is moved into the "OFF" position, systems which operate using switched voltage are effectively neutralized

This conserves battery voltage and makes transportation as we know it much more reliable

When the ignition switch is moved into the "ACCESSORY" or "AUXILAIRY" positions, switched voltage is supplied to limited systems most often associated with use during stationary use

Placing the ignition switch in the "START" position activates the starter and enables engine starting

The "RUN" position supplies voltage to virtually all switched voltage systems

The start position usually springs back to the "RUN" position after the key cylinder is released to prevent starter motor and/or flywheel ring gear damage

There are several tools which will be instrumental in attempting to successfully diagnose the conditions which contribute to this code being stored

A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in trying to perform a successful diagnosis

Gaining access to a manufacturer's wiring schematic will also prove necessary for successfully diagnosing this code.
Perform a careful visual inspection of all ignition switch wiring and connectors

Always retest the system after repairs are completed to ensure success.
If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data

This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored

Continue by clearing the code and operating the vehicle to see if it returns

This will help to determine whether or not the malfunction is intermittent.
After the codes are cleared, test drive the vehicle to see if the code returns

If the code fails to immediately return, you may have an intermittent condition

Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can even be attempted

If the code immediately returns, check for battery voltage and ground signals at the ignition switch

If either the ground or battery voltage circuits are open, use the digital volt/ohmmeter to check for continuity (disconnect all related control modules from the circuit before checking circuit resistance or controller damage may occur) and resistance in both circuits

Repair or replace system circuits/connectors as required and retest the system to ensure that repairs were successful

Pay particular attention to system fuses and fusible links and remember to locate the cause of fuse and fusible link failure to avoid repeated failures.
Using the manufacturer's wiring diagram for the ignition switch, test all related circuits for resistance and continuity and compare your findings with manufacturer's specifications

Repair or replace system circuitry, connectors, and/or components that fail to coincide with manufacturer's specs

Always retest the system afterward to ensure that the repair was successful.